1. Technical Field
The present invention relates to a short circuit detection circuit and short circuit detection method, in particular, to a short circuit detection circuit and a short circuit detection method for a multi-phase rectifier at alternator or Integrated Starter Generator (ISG) application.
2. Description of Related Art
A multi-phase rectifier of an alternator or an ISG is composed of many pairs of rectifying elements (e.g., diodes, MOSFETs, IGBTs, and etc.) to convert alternating current (AC) into direct current (DC) and then the direct current charges the battery connected to the multi-phase rectifier. When the multi-phase rectifier becomes short, it generates excessive heat loss causing safety issues (e.g., damaging the whole alternator). The multi-phase rectifier's short circuit detection is necessary to raise the alarm for this abnormal condition. In order to detect the multi-phase rectifier's short circuit, each current path of the multi-phase rectifier will be equipped with a short circuit detection element to detect whether the multi-phase rectifier is short circuit.
Generally speaking, short circuit detection methods for detecting whether a multi-phase rectifier is shorted out use either a sensing resistor or hall-effect sensor. For clarity, the following regards the rectifying element as a diode. For one diode which is configured in a current path, as shown in FIG. 1A, the sensing resistor R1 is configured in serial with the diode D1 so that the current I1 will flow through the diode D1 as well as the sensing resistor R1. Then the operational amplifier (op-amp) OP1 amplifies the voltage across the sensing resistor R1 to generate a detected signal Sd1. Next, the comparator CP1 receives the detected signal Sd1 and compares the detected signal Sd1 with a reference signal Vref1 (i.e., the short circuit threshold voltage) to output a result signal OUT1, so as to determine whether the diode D1 is short. Because the short circuit detection method has to add the additional sensing resistor R1 which is configured in the current path, it will cause (I12*R1) power loss in the current path. Furthermore, the sensing resistor R1 is required low resistance and high current operation generally and is usually expensive. For complete short circuit detection each multi-phase rectifier must have the above configuration respectively. So that, this will cause more power loss and cost.
Using the other method, as shown in FIG. 1B, the hall-effect sensor HF is configured near a current path of a diode D2 to detect a current I2 of the current path using the magnetic field measurement method and then generate a detected signal Sd2. Next, the comparator CP2 receives the detected signal Sd2 and compares the detected signal Sd2 with a reference signal Vref2 (i.e., the short circuit threshold voltage) to output a result signal OUT2 indicating whether the diode D2 is shorted out. Comparing the short circuit detection method using the hall-effect sensor with that of using the sensing resistor, the short circuit detection method using the hall-effect sensor has less power loss, but the hall-effect sensor HF is also expensive.
Therefore, if the power loss and the cost can be reduced effectively during the processing of the short circuit detection method, the efficiency of the multi-phase rectifier can be enhanced greatly.
To address the above issues, the inventor strives via associated experience and research to present the instant disclosure, which can effectively improve the constraints described above.